The present invention relates to a zero gravity robotic system and method for using same.
Material removal or deburring of work pieces has recently become a desirable application for industrial robots. Traditionally deburring has been a manual process due to all of the variables that must be controlled. Some of these variables include the selection of the abrasive to be used, the spindle speed of the tool, the contact angle of the tool against the work piece, and the force applied between the tool and the work piece.
In the case of robotic application of the tool to the work piece, it is important to maintain a precise control of the pressure of the tool against the part. However, with present systems, the movement of the robot often orients the tool in a way that causes gravity to act differently upon the tool. The effect of gravity can change the pressure of the tool against the work piece.
Most force devices presently available incorporate a spring or air cylinder component attached to a linear slide. When the linear slide is horizontally oriented, gravity has a negligible effect upon the magnitude of the force. However, when the tool is tipped gravity affects the magnitude of the force.
FIGS. 3A and 3B illustrate this phenomenon. In FIG. 3A, the force is applied horizontally against the work piece, and the effect of gravity is negligible.
However, in FIG. 3B, when the tool is tilted 30xc2x0, the net force on the work piece is the force applied by the slide plus gravity multiplied by the sine of 30xc2x0.
Thus in the linear slide application, gravity changes the net force which is applied to the work piece, depending upon the orientation of the tool with respect to gravity.
While this problem is encountered with deburring devices which utilize a rotating brush to remove burrs or foreign material from the work object, the problem also occurs in other types of robotic applications. For example it can occur during the application of a heat weld where the tool is pressed against the work piece. Another example is the application of pressure from a rotating drilling bit to the work piece. Another example would be the pressure applied during riveting. There are many other applications where the pressure between the tool and the work piece must be carefully controlled, and in these applications it is necessary to neutralize the effect of gravity on that pressure. Therefore a primary object of the present invention is the provision of a zero gravity robotic system that neutralizes the effect of gravity upon the pressure between the tool and the work piece.
A further object of the present invention is the provision of a zero gravity robotic system which operates rotationally around the center of gravity of the tool motor and which can be tipped at an angle without gravity affecting the force between the tool and the work piece.
A further object of the present invention is the provision of a zero gravity robotic system which utilizes a rotational motion to apply force between the tool and the work piece rather than a linear motion as in prior art devices.
A further object of the present invention is the provision of a zero gravity robotic system which utilizes a spring as a counterbalance to improve reaction sensitivity at low contact forces between the tool and the work piece.
A further object of the present invention is the. provision of a zero gravity robotic system which is economical to manufacture, durable in use and efficient in operation.
The foregoing objects may be achieved by a combination which includes a robotic arm having a distal end. Mounted on the distal end of the robotic arm is a motor having a rotatable arbor and a tool mounted to the arbor for rotation therewith about a tool axis. A pivot mechanism connects the motor and the tool to the distal end of the robotic arm for rotation about a motor axis which passes approximately through the center of gravity of the motor and the tool. A prime mover is connected to the distal end of the robotic arm and to the pivot mechanism for creating a rotational force to cause the pivotal movement of the motor about the motor axis. This results in the force of gravity having negligible effect upon the rotational force applied to the tool regardless of the orientation of the motor with respect to gravity.
According to one feature of the invention the tool axis is oriented perpendicular to the motor axis.
According to another feature of the invention the pivot mechanism comprises a lever member pivotally connected to the distal end of the robotic arm for rotation about the motor axis. A lever member is also attached to the motor.
According to another feature of the invention the prime mover is a fluid cylinder having an extensible rod. However, other types of prime movers could be used.
According to another feature of the invention a spring is attached to the pivot mechanism and the distal end of the robotic arm and provides a counterbalancing force to the force exerted by the fluid cylinder and the extensible rod.
The foregoing objects may be achieved by a method of rotatably mounting a motor having a work tool thereon to the distal end of a robotic arm for rotation about a motor axis which passes through the approximate center of gravity of the motor and the tool. A predetermined rotational force is applied to the motor and the work tool to cause the motor and the work tool to rotate about the motor axis whereby the passing of the motor axis through the approximate center of gravity will cause gravity to have a negligible effect upon the predetermined rotational force applied to the tool regardless of the orientation of the motor and the tool with respect to gravity.